a) eating animals is justified because we are omnivorous/carnivorous by nature, and,
b) who fucking cares anyway.
I don’t think it is “we don’t need ethics out there” as some might frame it.
I’d say we all have this collective naive ethics that killing sentient animals leaves bad tastes in the mouth, and I’d love not having to feel or think about it, but that cannot immediately mean it is, like, can be proven logically wrong.
Most humans are also fully capable and arguably evolved to do things like steal and murder each other, are those also justified simply because we're capable? And on the second point, the existence of OPs article and the comments around this one indicate that some people do care.
My point here to be more clear is that we simply don't need to consume animals, and that the taste pleasure of eating them doesn't justify their death. Humans are animals too, and the success of our species doesn't require intense suffering of another.
But it would. At least we have, as a society, decided that it would. But this is rather flexible, since in older times, as well as in some cultures, wanton animal cruelty is accepted. I guess that the argument for prohibiting cruelty to animals is that it is good to prohibit behavior which we believe to be detrimental to the person doing it. I.e. it’s not prohibited to protect the dog, it’s prohibited to protect you from becoming a cruel bastard and turning around and being toxic in human society. Whether this actually is a valid argument is, of course, subjective and debatable, which is why cultures differ on this point.